Per-Link Parallel and Distributed Hybrid Beamforming for Multi-User Multi-Cell Massive MIMO Millimeter Wave Full Duplex

This paper presents two hybrid beamforming (HYBF) designs for a multi-user multi-cell millimeter (mmWave) full-duplex (FD) system. The base stations (BSs) and the users are assumed to be suffering from the limited dynamic range (LDR) noise. Firstly, we present a centralized HYBF (C-HYBF) scheme based on alternating optimization. In general, the complexity of C-HYBF schemes scales quadratically as a function of the number of users, which is very undesirable. Moreover, tremendous computational power is required to optimize numerous variables jointly in FD. Another major drawback is that huge communication overhead is also required to transfer complete channel state information (CSI) to the central node every channel coherence time. To overcome these drawbacks, we present a very low-complexity and highly scalable cooperative per-link parallel and distributed (P$\&$D)-HYBF scheme. It allows each FD BS to update the beamformers for its users independently in parallel on different computational processors. Its complexity scales only linearly as the network size grows, making it desirable for the next generation of large and dense mmWave FD networks. Simulation results show that both designs significantly outperform the fully digital half-duplex (HD) system with only a few radio-frequency (RF) chains, achieve similar performance, and the P$\&$D-HYBF requires considerably less execution time.